Method for heat treatment of a metal component

ABSTRACT

The invention relates to a method for heat treating a metal component. The invention relates in particular to an application in the partial hardening of optionally pre-coated components made of high-strength manganese-boron steel. With the method, at least one first sub-region of the component is convectively cooled by means of at least one nozzle, which discharges a fluid stream to the first sub-region so that a temperature difference of at least 100 K is set between the at least one first sub-region and at least one second sub-region of the component, wherein the at least one nozzle is operated with a positive pressure of at least 2 bar.

The invention relates to a method for heat treating a metal component.The invention is used, in particular, during the partial hardening ofoptionally pre-coated components made of a high-strength manganese-boronsteel.

To produce safety-relevant vehicle body parts made of sheet steel, it isgenerally required to harden the sheet steel while or after it is formedinto the body part. For this purpose, a heat treatment method referredto as “press hardening” has established itself. In this process, thesheet steel, which is generally provided in the form of a blank, isinitially heated in a furnace and thereafter is cooled during theforming operation in a press, whereby it is hardened.

There has been an endeavor for several years now to use press hardeningto provide body parts of motor vehicles, such as A and B pillars, sideimpact protection beams in doors, sills, frame parts, bumpers,transverse beams for the floor and roof, and front and rear longitudinalbeams, which have differing strengths in sub-regions, so that the bodypart can partially fulfill different functions. For example, the centerregion of a B pillar of a vehicle should have high strength so as toprotect the occupants in the event of a side impact. At the same time,the upper and lower end regions of the B pillar should havecomparatively low strength, so as to be able to absorb deformationenergy during a side impact, while enabling easy connectability to otherbody parts during the installation of the B pillar.

So as to create such a partially hardened body part, it is necessary forthe hardened component to have differing material microstructures orstrength properties in the sub-regions. So as to set differing materialmicrostructures or strength properties after hardening, the sheet steelto be hardened may, for example, already be provided with differingsheet sections that are joined to one another or may be partially cooleddifferently in the press.

As an alternative or in addition, there is the option to subject thesheet steel to be hardened to partially differing heat treatmentprocesses prior to the cooling and forming steps in the press. In thisconnection, for example, it possible to heat only sub-regions of thesheet steel to be hardened in which a transformation toward hardermicrostructures, such as martensite, is to be effectuated. This kind ofprocess control, however, generally has the disadvantage that the inwarddiffusion of a coating, which is usually to be applied to the surface ofthe sheet steel to protect against scaling, such as an aluminum siliconcoating, cannot be efficiently integrated into the heat treatmentprocess. Furthermore, the option exists to carry out the partial heattreatment by way of contact plates, which are designed to partiallycontrol the temperature of the sheet steel by way of heat conduction.This, however, requires a certain contact time with the plates, which isusually longer than a (minimum) cycle time achievable by the downstreampress. Furthermore, the coordination between a certain contact time andthe cycle time at the press generally makes it more difficult tointegrate corresponding temperature control stations into a presshardening line on an industrial scale, where production fluctuationsduring operation are in general unavoidable.

Proceeding from this, it is the object of the present invention to atleast partially solve the problems described with regard to the priorart. In particular, a method for heat treating a metal component is tobe provided, which allows a partially differing heat treatment of thecomponent to be carried out on an industrial scale, and in particular asefficiently as possible. Moreover, the method, in particular, is to helpreduce the influence of the process segment of the heat treatmentprocess located upstream of the press on the cycle time of the overallheat treatment process.

These objects are achieved by the features of the independent claims.Further advantageous embodiments of the solution disclosed herein aredescribed in the dependent claims. It should be noted that the featureslisted individually in the dependent claims can be combined with oneanother in any arbitrary, technologically meaningful manner and definefurther embodiments of the invention. Furthermore, the featuresdescribed in the claims are specified and explained in greater detail inthe description, wherein further preferred embodiments of the inventionare presented.

In a method according to the invention for the (partially differing)heat treatment of a metal component, at least one first sub-region ofthe component (which is more ductile in the fully treated component) isconvectively cooled by means of at least one nozzle, which discharges afluid stream toward the first sub-region, so that a temperaturedifference of at least 100 K [Kelvin] is set between the at least onefirst sub-region and at least one second sub-region of the component(which is comparatively harder in the fully treated component), whereinthe at least one nozzle is operated at a positive pressure of at least 2bar.

The disclosed method is used, in particular, for the targeted componentzone-specific heat treatment of a (steel) component or for settingdifferent microstructures in a targeted manner in various sub-regions ofa steel component. Preferably, the method is used to partially hardenoptionally pre-coated components made of a (high-strength)manganese-boron steel.

In a particularly advantageous manner, the disclosed method makes itpossible to reliably carry out a partially differing heat treatment of acomponent even on an industrial scale. In particular by cooling the atleast one first sub-region of the component by means of at least onenozzle operated at a positive pressure of at least 2 bar, the influenceof the process segment of the heat treatment process located upstream ofthe press on the cycle time of the entire heat treatment process can bereduced. In other words, cooling the at least one first sub-region ofthe component by means of at least one nozzle operated at a positivepressure of at least 2 bar particularly advantageously allows the atleast one first sub-region of the component to be cooled very quickly byat least 100 K, and in particular so quickly that a cooling period isless than or equal to a cycle time of a downstream press hardening tool(press cycle). It is not possible to achieve such short cooling periods,in particular, when using fans, which can be used to generate a(cooling) air stream toward a component surface.

Preferably, a cooling period during which the at least one firstsub-region of the component is cooled by way of convection or by meansof the nozzle is less than fifteen seconds, in particular less than tenseconds or even less than five seconds, and particularly preferably lessthan three seconds.

The metal component is preferably a metal blank, a sheet steel or an atleast partially preformed semi-finished product. The metal component ispreferably made with or of a (hardenable) steel, for example a boron(manganese) steel, such as that with the designation 22 MnB5. It isfurthermore preferred that the metal component is provided or pre-coatedwith a (metal) coating at least to a large degree. For example, themetal coating may be a coating (predominantly) comprising zinc, or acoating (predominantly) comprising aluminum and/or silicon, and inparticular what is known as an aluminum/silicon (Al/Si) coating.

The at least one nozzle is preferably disposed in a temperature controlstation, wherein the temperature control station is particularlypreferably located downstream of a first furnace and/or a secondfurnace. The at least one nozzle, and in particular an outlet of thenozzle, may be oriented toward the first sub-region. Moreover, the atleast one nozzle, and in particular an inlet of the nozzle, may beconnected to a fluid source. The fluid source may be a tank in which thefluid forming the fluid stream is stored in compressed form. The fluidmay be, for example, (compressed) air, nitrogen, water or a mixturethereof, for example.

The fluid is preferably compressed air and/or the fluid stream ispreferably a (compressed) air stream. The at least one nozzle ispreferably at least one compressed air nozzle. In other words, the atleast one nozzle is preferably operated with compressed air. To providethe compressed air, the at least one nozzle, and in particular an inletof the nozzle, may be connected to at least one compressor. In otherwords, compressed air having a positive pressure of at least 2 bar canbe provided by means of at least one compressor. Furthermore, thecompressed air thus provided can be supplied to the at least one nozzle.This may take place prior to, simultaneously with and/or at leastpartially simultaneously with the cooling by means of the at least onenozzle. If multiple nozzles are provided, these can be connected to ashared compressor. Preferably, the compressor is provided and configuredfor supplying compressed air having a positive pressure of at least 2bar to the at least one compressed air nozzle. For this purpose, forexample, the compressor can provide a positive (system) pressure of atleast 2 bar, which is preferably kept available or stored in a pressure(or compressed air) reservoir. Particularly preferably, an (appropriate)pressure reservoir is disposed in a piping system connecting thecompressor to the at least one compressed air nozzle and/or is connectedto the piping system between the compressor and the at least onecompressed air nozzle. Furthermore, at least one activatable valve,which is actuated, and in particular opened and closed, in keeping witha desired cooling period and/or a desired (compressed air) volume flow,can be disposed between the compressor and the at least one compressedair nozzle. Furthermore, it is advantageously possible to form apreferably activatable valve between the compressor and the at least onecompressed air nozzle, by means of which the flow rate of the fluidstream through the nozzle can be adapted, so that the volume flowthrough the nozzle can be adapted, for example as a function of theoperating situation and/or as a function of properties of the component,such as the thickness of the component.

Preferably, the (or each) nozzle is shaped in the manner of a fannozzle. It is furthermore preferred when multiple nozzles are provided,which particularly preferably are arranged so as to form a nozzle array.In particular, the shape of the nozzle array and/or the arrangement ofthe multiple nozzles is adapted to the (desired) geometry of the atleast one first sub-region of the component.

The cooling preferably takes place by means of a plurality of nozzles,and in particular by means of at least five or even at least tennozzles, which can be activated individually or in groups and which, inparticular, can be supplied with a (certain) fluid volume flow. Thenozzles are preferably activated as a function of time. It isfurthermore preferred that the nozzles are activated (individually or ingroups) in such a way that one or more temperature differences are setdeliberately between sub-regions of the component, for example betweenthe at least one first sub-region and the at least one secondsub-region. Moreover, the nozzles can be activated (individually or ingroups) in such a way that ambient influencing conditions in thetemperature control station, which can act on the component upon leavingthe temperature control station, can be compensated for. Such acompensation, which in particular shall be understood to mean aprevention, may take place in such a way, for example, that a region ofthe component located closer to the edge, and in particular a region ofthe at least one first sub-region located closer to the component edge,is cooled to a lesser degree than a region of the component locatedfurther away from the edge, and in particular than a region of the atleast one first sub-region of the component located further away fromthe component edge, so as to take into consideration or even(substantially) compensate for faster cooling of the component in theedge regions thereof, which may possibly take place upon leaving thetemperature control station, in particular in the heat exchange with thesurrounding area.

As a result of the convective cooling, a temperature difference of atleast 100 K, preferably of at least 150 K or even of at least 200 K isset between the at least one first sub-region and at least one secondsub-region of the component. After cooling, the component has partiallydiffering (component) temperatures, wherein a temperature difference isset between a first temperature of the at least one first sub-region anda second temperature of the at least one second sub-region of thecomponent. Moreover, it is possible to set several (different)temperature differences between sub-regions of the component. It ispossible, for example, to set three or more sub-regions in thecomponent, each having a temperature different from the others. Thepartially differing temperatures can cause differing microstructuresand/or strength properties to be produced in the component, inparticular during a possibly following quenching process, such as duringa press hardening operation.

The at least one nozzle is operated at a positive pressure of at least 2bar, preferably of at least 2.5 bar, particularly preferably of at least3.5 bar or even of at least 5 bar. Preferably, a fluid forming the fluidstream has a positive pressure of at least 2 bar, preferably of at least2.5 bar, particularly preferably of at least 3.5 bar or even of at least5 bar, at an inlet of the at least one nozzle, in particular during acooling period. In other words, this means, in particular, that thepositive pressure that is used to operate the at least one nozzle can bemeasured on an inlet of the at least one nozzle. When the nozzle isconnected to a pressure (or compressed air) reservoir, the positivepressure that is used to operate the at least one nozzle will refer inparticular to the positive pressure kept available or stored in thepressure reservoir. A positive pressure here shall be understood to meana pressure that is determined relative to the ambient pressure oratmospheric pressure.

The fluid stream may be accelerated while flowing through the at leastone nozzle. Preferably, the fluid stream exits the at least one nozzlewith an exit velocity of approximately the sound velocity. It isfurthermore preferred that the fluid stream discharged by means of theat least one nozzle applies a blowing pressure of at least 3000 Pa[Pascal] or N/m² [Newton per square meter] onto a surface of thecomponent in the at least one first sub-region of the component.Preferably, the cooling by means of the at least one nozzle sets acooling rate of at least 100 K/s [Kelvin per second] in the at least onefirst sub-region of the component.

According to an advantageous embodiment, it is proposed that, prior tocooling, at least the at least one first sub-region of the component isheated by at least 500 K, preferably by at least 600 K or even by atleast 800 K. Preferably, prior to cooling, the at least one firstsub-region of the component is heated by means of the at least onenozzle in a first furnace and/or by way of radiant heat and/orconvection. It is furthermore preferred that the cooling takes place bymeans of the at least one nozzle in a temperature control stationlocated downstream of a first furnace.

According to an advantageous embodiment, it is proposed that, aftercooling, at least the at least one first sub-region of the component isheated by at least 100 K, preferably by at least 150 K or even by atleast 200 K. Preferably, after cooling, the at least one firstsub-region of the component is heated by means of the at least onenozzle in a second furnace and/or by way of radiant heat and/orconvection. It is particularly preferred when the second furnace islocated downstream of the temperature control station.

According to a further aspect, a method for the (partially differing)heat treatment of a metal component comprising at least the followingsteps is disclosed:

-   -   a) heating the component in a first furnace, in particular by        way of radiant heat and/or convection;    -   b) moving the component into a temperature control station;    -   c) convectively (partially) cooling at least one first        sub-region of the component in the temperature control station        by means of at least one nozzle discharging a fluid stream        toward the first sub-region, wherein a temperature difference is        set between the at least one first sub-region and at least one        second sub-region of the component, and wherein the at least one        nozzle is operated at a positive pressure of at least 2 bar.

The indicated sequence of method steps a), b) and c) is derived during aregular process of the method. Individual or multiple of the methodsteps may be carried out simultaneously, consecutively and/or at leastpartially simultaneously.

In step a), the (entire) component is heated in a first furnace.Preferably, the component is heated homogeneously or uniformly in thefirst furnace. It is furthermore preferred that the component is heatedin the first furnace (exclusively) by way of radiant heat, for exampleby at least one electrically operated heating element (not makingphysical or electrical contact with the component), such as a heatingloop and/or a heating wire, and/or by at least one (gas-heated) radianttube. The first furnace can be a continuous furnace or a batch furnace.

In step b), the component is moved, in particular, from the firstfurnace into a temperature control station. For this purpose, atransport unit may be provided, for example at least comprising a rollertable and/or an (industrial) robot. Preferably, the component travels adistance of at least 0.5 m [meters] from the first furnace to thetemperature control station. The component may be guided in contact withthe ambient area or within a protective atmosphere.

In step c), at least one first sub-region of the component is (actively)cooled in the temperature control station. Preferably, an input ofthermal energy into the at least one second sub-region of the componenttakes place in the temperature control station, simultaneously or atleast partially simultaneously with the cooling of the at least onefirst sub-region of the component. Preferably, the at least one secondsub-region of the component is subjected in the temperature controlstation (exclusively) to heat radiation, which is generated and/orirradiated, for example, by at least one electrically operated or heatedheating element, which is disposed in particular in the temperaturecontrol station (and does not make contact with the component), such asa heating loop and/or a heating wire, and/or by at least one(gas-heated) radiant tube, which is, in particular, disposed in thetemperature control station.

The input of thermal energy into the at least one second sub-region ofthe component can preferably take place in the temperature controlstation in such a way that a decrease in the temperature of the at leastone second sub-region and/or a cooling rate of the at least one secondsub-region is at least reduced while the component remains in thetemperature control station. This process control is in particularadvantageous when the component was heated in step a) to a temperatureabove the Ac3 temperature. As an alternative, the input of thermalenergy into the at least one second sub-region of the component in thetemperature control station may take place in such a way that the atleast one second sub-region of the component is heated (considerably),in particular by at least approximately 50 K. This process control is inparticular advantageous when the component was heated in step a) to atemperature below the Ac3 temperature, or even below the Ac1temperature.

According to an advantageous embodiment, it is proposed that the methodfurthermore comprises at least the following steps:

-   -   d) moving the component from the temperature control station        into a second furnace; and    -   e) heating at least the at least one first sub-region of the        component in the second furnace by at least 100 K [Kelvin], in        particular by way of radiant heat and/or convection.

In step d), the component is moved from the temperature control stationinto a second furnace. For this purpose, a transport unit may beprovided, for example at least comprising a roller table and/or an(industrial) robot. The component preferably travels a distance of atleast 0.5 m from the temperature control station to the second furnace.The component may be guided in contact with the ambient area or within aprotective atmosphere. Preferably, the component is transferred directlyinto the second furnace immediately upon having been removed from thetemperature control station. The second furnace can be a continuousfurnace or batch furnace.

In step e), at least the at least one first sub-region of the componentis heated in the second furnace by at least 100 K, preferably by atleast 150 K or even by at least 200 K. In other words, another heatingprocess takes place in the second furnace, wherein at least thepreviously (actively) cooled at least one first sub-region is heated byat least 100 K. Preferably, at least the at least one first sub-regionof the component is heated in the second furnace (exclusively) by way ofradiant heat, for example by at least one electrically operated heatingelement (not making contact with the component), such as a heating loopand/or a heating wire, and/or by at least one (gas-heated) radiant tube.It is furthermore preferred that in step e), in particularsimultaneously or at least partially simultaneously with the heating ofthe at least one first sub-region, the at least one second sub-region ofthe component is heated in the second furnace by at least 50 K,particularly preferably by at least 70 K or even by at least 100 K, inparticular (exclusively) by way of radiant heat. Particularlypreferably, the at least one second sub-region of the component isheated in step e) to a temperature above the Ac1 temperature or evenabove the Ac3 temperature. Alternatively, in step e), in particularsimultaneously or at least partially simultaneously with the heating ofthe at least one first sub-region, a decrease in the temperature of theat least one second sub-region and/or a cooling rate of the at least onesecond sub-region is at least reduced while the component remains in thesecond furnace.

In other words, in step e) an input of thermal energy, in particular byway of radiant heat, into the entire component may take place. Forexample, the second furnace may (for this purpose) include a furnaceinterior, which in particular is heated (exclusively) by way of radiantheat, in which preferably a substantially uniform inside temperatureprevails. The input of thermal energy into the at least one firstsub-region of the component in the second furnace preferably takes placein such a way that the temperature of the at least one first sub-regionis increased by at least 100 K, preferably by at least 120 K,particularly preferably by at least 150 or even by at least 200 K.

The input of thermal energy into the at least one second sub-region ofthe component in the second furnace can preferably take place in such away that a decrease in the temperature of the at least one secondsub-region and/or a cooling rate of the at least one second sub-regionis at least reduced while the component remains in the second furnace.This process control is in particular advantageous when the componentwas heated in step a) to a temperature above the Ac3 temperature. As analternative, the input of thermal energy into the at least one secondsub-region of the component in the second furnace can take place in sucha way that the at least one second sub-region of the component is atleast (considerably) heated, in particular by at least 50 K,particularly preferably by at least 70 K or even by at least 100 K,and/or is heated to a temperature above the Ac1 temperature or evenabove the Ac3 temperature. This process control is in particularadvantageous when the component was heated in step a) to a temperaturebelow the Ac3 temperature, or even below the Ac1 temperature.

According to a further advantageous embodiment, it is proposed that themethod furthermore comprises at least the following steps:

-   -   f) moving the component from the temperature control station or        from the second furnace into a press hardening tool; and    -   g) forming and cooling the component in the press hardening        tool.

Preferably, the moving in step f) takes place by means of a transportdevice, for example at least comprising a roller table and/or an(industrial) robot. Preferably, the component travels a distance of atleast 0.5 m from the second furnace to the press hardening tool. Thecomponent may be guided in contact with the ambient area or within aprotective atmosphere. Preferably, the component is transferred directlyinto the press hardening tool immediately upon having been removed fromthe second furnace.

According to an advantageous embodiment, it is proposed that thecomponent is heated in step a) to a temperature below the Ac3temperature, or even below the Ac1 temperature. The Ac1 temperature isthe temperature at which the transformation from ferrite to austenitebegins when a metal component, and in particular a steel component, isheated.

According to an (alternative) advantageous embodiment, it is proposedthat the component is heated in step a) to a temperature above the Ac3temperature. The Ac3 temperature is the temperature at which thetransformation from ferrite to austenite ends or has been (entirely)completed when a metal component, and in particular a steel component,is heated.

According to an advantageous embodiment, it is proposed that the atleast one first sub-region is cooled in step c) by way of convection toa temperature below the Ac1 temperature. Preferably, the at least onefirst sub-region is cooled in step c), in particular by way ofconvection, to a temperature below 550° C. [° Celsius] (823.15 K),particularly preferably below 500° C. (773.15 K) or even below 450° C.(723.15 K).

The details, features and advantageous embodiments described inconnection with the method disclosed first may also be presentaccordingly with the method disclosed here, and vice versa. In thisregard, all the comments provided there to further characterize thefeatures are hereby incorporated by reference.

So as to achieve the described object(s), a method for the (partiallydiffering) heat treatment of a metal component comprising at least thefollowing steps could also be used:

-   -   a) heating the component in a first furnace, in particular by        way of radiant heat and/or convection;    -   b) moving the component into a temperature control station;    -   c) convectively (partially) cooling at least one first        sub-region of the component in the temperature control station        by means of at least one nozzle discharging a fluid stream        toward the first sub-region, wherein a temperature difference is        set between the at least one first sub-region and at least one        second sub-region of the component, and wherein the at least one        nozzle is operated with compressed air.

The details, features and advantageous embodiments described inconnection with the methods disclosed first may also be presentaccordingly with the method disclosed here, and vice versa. In thisregard, all the comments provided there to further characterize thefeatures are hereby incorporated by reference.

According to a further aspect, a device for heat treating a metalcomponent is disclosed, comprising at least the following:

-   -   a first furnace heatable in particular by way of radiant heat        and/or convection;    -   a temperature control station located downstream of the first        furnace, in which at least one nozzle is disposed or held, which        is provided to discharge a fluid for cooling at least one first        sub-region of the component and configured, in particular, such        that a temperature difference can be set between the at least        one first sub-region and at least one second sub-region of the        component, wherein the at least one nozzle is preferably        provided and configured to be operated at a positive pressure of        at least 2 bar.    -   a second furnace located downstream of the temperature control        station and heatable, in particular, by way of radiant heat        and/or convection, which is provided and configured for heating        at least the at least one first sub-region of the component by        at least 100 K.

The device may be used to carry out a method disclosed herein. Thedevice is preferably provided and configured for carrying out the methoddisclosed herein. Preferably, an electronic control unit, which issuitable for carrying out a method disclosed herein and configuredtherefor, is assigned to the device. Particularly preferably, thecontrol unit comprises at least one program-controlled microprocessorand an electronic memory for this purpose, a control program that isprovided and configured for carrying out a method disclosed herein beingstored in the memory.

According to a further advantageous embodiment, it is proposed that atleast the first furnace or the second furnace is a continuous furnace ora batch furnace. Preferably, the first furnace is a continuous furnace,and in particular a roller hearth furnace. The second furnace isparticularly preferably a continuous furnace, and in particular a rollerhearth furnace, or a batch furnace, and in particular a multi-levelbatch furnace comprising at least two chambers disposed on top of oneanother. The second furnace preferably includes a furnace interior,which in particular is heatable (exclusively) by way of radiant heat, inwhich preferably a substantially uniform inside temperature can be set.In particular when the second furnace is designed as a multi-level batchfurnace, multiple such furnace interiors may be present corresponding tothe number of chambers.

Preferably, (exclusively) radiant heat sources are disposed in the firstfurnace and/or in the second furnace. It is particularly preferred whenat least one electrically operated heating element (not making contactwith the component), such as at least one electrically operated heatingloop and/or at least one electrically operated heating wire, is disposedin a furnace interior of the first furnace and/or in a furnace interiorof the second furnace. As an alternative or in addition, at least one,in particular gas-heated, radiant tube may be disposed in the furnaceinterior of the first furnace and/or the furnace interior of the secondfurnace. Preferably, multiple radiant tube gas burners or radiant tubesinto each of which at least one gas burner burns are disposed in thefurnace interior of the first furnace and/or the furnace interior of thesecond furnace. It is particularly advantageous when the inner region ofthe radiant tubes into which the gas burners burn is atmosphericallyseparated from the furnace interior, so that no combustion gases orexhaust gases can reach the furnace interior, and thus influence thefurnace atmosphere. Such a system is also referred to as “indirect gasheating.”

At least one nozzle, which is provided and configured for discharging afluid, is disposed or held in the temperature control station. The atleast one nozzle can be operated at a positive pressure of at least 2bar. The device can furthermore comprise at least one compressor, whichis preferably assigned to the temperature control station, in particularfor providing the positive pressure. The compressor can be (fluidically)connected to the at least one nozzle, and in particular to an inlet ofthe nozzle. Preferably, the device comprises at least one pressure (orcompressed air) reservoir, which is provided and configured for keepingpressure provided by means of the compressor available or storing thispressure. The pressure reservoir is preferably assigned to thetemperature control station. It is furthermore preferred when thepressure reservoir is disposed in a piping system connecting thecompressor to the at least one compressed air nozzle and/or is connectedto the piping system between the compressor and the at least onecompressed air nozzle. The compressor is preferably provided andconfigured for providing the fluid forming the fluid stream at apositive pressure of at least 2 bar. The compressor is preferably areciprocating compressor, a rotary compressor, in particular ascrew-type compressor, or a turbo compressor, which particularlypreferably is designed with a plurality of rotatably drivable blades (ofat least one rotor) and a plurality of fixed blades (of at least onestator).

As an alternative or in addition, a source for a pressurized fluid,which can be connected to the at least one nozzle, may be providedinstead of or in addition to a compressor. This is preferably a sourcein which a liquefied gas is vaporized, for example by way of anappropriate heat exchanger which causes the liquefied gas (such asliquefied nitrogen) to vaporize, for example under ambient air. Thevaporized gas can then preferably be supplied to a compressor forincreasing the pressure, if the gas pressure at the outlet of the sourceshould be too low.

Preferably, (moreover) at least one heating unit is disposed in thetemperature control station. The heating unit is preferably provided andconfigured for inputting thermal energy into the at least one secondsub-region of the component. Particularly preferably, the heating unitis disposed and/or oriented in the temperature control station in such away that the input of thermal energy into the at least one secondsub-region of the component can be carried out simultaneously, or atleast partially simultaneously, with the cooling of the at least onefirst sub-region of the component by means of the at least one nozzle.Preferably, the heating unit (exclusively) comprises at least oneradiant heat source. Particularly preferably, the at least one radiantheat source is designed with at least one electrically operated heatingelement (not making contact with the component), such as at least oneelectrically operated heating loop and/or at least one electricallyoperated heating wire. As an alternative or in addition, at least onegas-heated radiant tube can be provided as the radiant heat source.

Furthermore, the device can comprise a press hardening tool, which islocated downstream of the second furnace. The press hardening tool is,in particular, provided and configured for simultaneously, or at leastpartially simultaneously, forming and (at least partially) quenching thecomponent.

The details, features and advantageous embodiments described inconnection with the methods may also be present accordingly with thedevice disclosed herein, and vice versa. In this regard, all thecomments provided there to further characterize the features are herebyincorporated by reference.

According to a further aspect, a use of at least one nozzle operated ata positive pressure of at least 2 bar for convectively cooling at leastone first sub-region of a metal component is proposed, wherein thenozzle is used in such a way that a temperature difference of at least100 K is set between the at least one first sub-region and at least onesecond sub-region of the component.

The details, features and advantageous embodiments described above inconnection with the methods and/or the device may also be presentaccordingly with the use disclosed herein, and vice versa. In thisregard, all the comments provided there to further characterize thefeatures are hereby incorporated by reference.

The invention and the technical environment will be described in moredetail hereafter based on the figures. It should be noted that theinvention shall not be limited by the shown exemplary embodiments. Inparticular, it is also possible, unless explicitly described otherwise,to extract partial aspects of the subject matter described in thefigures, and to combine these with other components and/or findings fromother figures and/or the present description. In the schematic drawings:

FIG. 1 shows a diagram of a device that can be used to carry out amethod according to the invention;

FIG. 2 shows a detailed view of the device from FIG. 1;

FIG. 3 shows a time-temperature curve achievable by means of a methodaccording to the invention; and

FIG. 4 shows a further time-temperature curve achievable by means of amethod according to the invention.

FIG. 1 schematically shows a device 12 for heat treating a metalcomponent 1, which can be used to carry out a method according to theinvention. The device 12 comprises a first furnace 7, a temperaturecontrol station 8, a second furnace 9, and a press hardening tool 11.The device 12 represents a hot forming line for press hardening here.

The temperature control station 8 is located (directly) downstream ofthe first furnace 7, so that a component 1 to be treated by means of thedevice 12 can be transferred directly into the temperature controlstation 8 upon leaving the first furnace 7. Furthermore, the secondfurnace 9 is located (directly) downstream of the temperature controlstation 8, and the press hardening tool 11 is located (directly)downstream of the second furnace 9.

FIG. 2 schematically shows a detailed view of the device from FIG. 1.FIG. 2 shows the temperature control station 8 of the device from FIG. 1in more detail. A nozzle 3, which discharges a fluid stream 4 toward afirst sub-region 2 of the component so as to (actively) cool this firstsub-region 2 by way of convection, is disposed in the temperaturecontrol station 8. By way of example, the nozzle 3 is operated at apositive pressure of 5 bar. For this purpose, the nozzle is connected onthe inlet side to a compressor 13. Moreover, a heating unit 11, which isprovided and configured for inputting thermal energy into a secondsub-region 6 of the component 1, is disposed in the temperature controlstation 8. For this purpose, the heating unit 11 is designed as anelectrically operated heating wire, for example.

FIG. 3 schematically shows a time-temperature curve achievable by meansof a method according to the invention. The temperature T of the metalcomponent is, or the temperatures T of the at least one first sub-regionand of the at least one second sub-region of the component are, plottedagainst the time t.

According to the time-temperature curve shown in FIG. 3, the metalcomponent 1 is first uniformly heated to a temperature below the Ac1temperature up until the point in time t₁. By way of example, thisheating takes place in a first furnace 2 here. Between the points intime t₁ and t₂, the metal component is transferred from the firstfurnace into a temperature control station. The component temperaturemay decrease slightly during this process, for example due to heatemission to the surrounding area.

Between the points in time t₂ and t₃, at least one first sub-region ofthe component is (actively) cooled in the temperature control station.This is illustrated in FIG. 3 based on the bottom time-temperature curvebetween the points in time t₂ and t₃. At the same time, at least onesecond sub-region of the component is (slightly) heated in thetemperature control station. This is illustrated in FIG. 3 based on thetop time-temperature curve between the points in time t₂ and t₃. In thisway, a temperature difference 5 is set in the temperature controlstation between the at least one first sub-region and at least onesecond sub-region of the component.

Between the points in time t₃ and t₄, the component is transferred fromthe temperature control station into a second furnace different from thefirst furnace. The partially differing temperatures set in thetemperature control station may decrease slightly during this process,for example due to heat emission to the surrounding area.

The component is heated in the second furnace from the point in time t₄to the point in time t₅ in such a way that the temperature of the atleast one first sub-region of the component is increased by at least 150K. Furthermore, the heating in the second furnace takes place in such away that, at the same time, the temperature of the at least one secondsub-region of the component is brought to a temperature above the Ac3temperature.

Between the points in time t₅ and t₆, the component is transferred fromthe second furnace into a press hardening tool. The partially differingtemperatures set in the second furnace may decrease slightly during thisprocess, for example due to heat emission to the surrounding area.

From the point in time t₆ until the end of the process, the (entire)component is quenched in the press hardening tool. It is possible for amartensitic microstructure to be produced at least partially or evenpredominantly in the at least one second sub-region of the component,which has comparatively high strength and comparatively low ductility.Essentially no transformation has taken place in the at least one firstsub-region of the component since the at least one first sub-region ofthe component has not exceeded the Ac1 temperature at any point duringthe process, so that a predominantly ferritic microstructure remains inthe at least one first sub-region of the component, which hascomparatively low strength and comparatively high ductility.

FIG. 4 schematically shows a further time-temperature curve achievableby means of a method according to the invention. Initially, the metalcomponent is uniformly heated to a temperature above the Ac3 temperatureup until the point in time t₁. By way of example, this heating takesplace in a first furnace here.

Between the points in time t₁ and t₂, the metal component is transferredfrom the first furnace into a temperature control station. The componenttemperature may decrease slightly during this process. Between thepoints in time t₂ and t₃, at least one first sub-region of the componentis (actively) cooled in the temperature control station. This isillustrated in FIG. 4 based on the bottom time-temperature curve betweenthe points in time t₂ and t₃. At the same time, the temperature of atleast one second sub-region of the component may decrease slightly inthe temperature control station. This is illustrated in FIG. 4 based onthe top time-temperature curve between the points in time t₂ and t₃.This (passive) decrease in temperature in the at least one secondsub-region of the component has a considerably lesser cooling rate thanthe simultaneous (active) cooling of the at least one first sub-regionof the component. It is apparent from FIG. 4 that a temperaturedifference 5 is set between the at least one first sub-region and atleast one second sub-region of the component in the temperature controlstation.

Between the points in time t₃ and t₄, the component is transferred fromthe temperature control station into a second furnace different from thefirst furnace. The partially differing temperatures set in thetemperature control station may decrease slightly during this process.

The component is heated in the second furnace from the point in time t₄to the point in time t₅ in such a way that the temperature of the atleast one first sub-region of the component is increased by at least 150K. Moreover, the heating in the second furnace takes place in such a waythat, at the same time, a cooling rate of the at least one secondsub-region of the component is reduced compared to a cooling rate duringheat emission to the surrounding area.

Between the points in time t₅ and t₆, the component is transferred fromthe second furnace into a press hardening tool. The partially differingtemperatures set in the second furnace may decrease slightly during thisprocess, for example due to heat emission to the surrounding area.

From the point in time t₆ until the end of the process, the (entire)component is quenched in the press hardening tool. It is possible for amartensitic microstructure to be produced at least partially or evenpredominantly in the at least one second sub-region of the component,which has comparatively high strength and comparatively low ductility.It is possible for a bainitic microstructure to be produced at leastpartially or even predominantly in the at least one first sub-region ofthe component, which has comparatively low strength and comparativelyhigh ductility.

LIST OF REFERENCE NUMERALS

1 component

2 first sub-region

3 nozzle

4 fluid stream

5 temperature difference

6 second sub-region

7 first furnace

8 temperature control station

9 second furnace

10 press hardening tool

11 heating unit

12 device

13 compressor

1. A method for heat treating a metal component, wherein the methodcomprising: convectively cooling at least one first sub-region of thecomponent by means of at least one nozzle discharging a fluid streamtoward the first sub-region, so that a temperature difference of atleast 100 K is set between the at least one first sub-region and atleast one second sub-region of the component, the at least one nozzlebeing operated at a positive pressure of at least 2 bar.
 2. The methodaccording to claim 1, further comprising, prior to cooling, heating atleast the at least one first sub-region of the component by at least 500K.
 3. The method according to claim 1, further comprising, aftercooling, heating at least the at least one first sub-region of thecomponent by at least 100 K.
 4. A method for heat treating a metalcomponent, comprising at least the following steps: a) heating thecomponent in a first furnace; b) moving the component into a temperaturecontrol station; c) convectively cooling at least one first sub-regionof the component in the temperature control station by means of at leastone nozzle discharging a fluid stream toward the first sub-region,wherein a temperature difference is set between the at least one firstsub-region and at least one second sub-region of the component, andwherein the at least one nozzle is operated at a positive pressure of atleast 2 bar.
 5. The method according to claim 4, the method furthermorefurther comprising at least the following steps: d) moving the componentfrom the temperature control station into a second furnace; and e)heating at least the at least one first sub-region of the component inthe second furnace by at least 100 K.
 6. The method according to claim4, further comprising at least the following steps: f) moving thecomponent from the temperature control station or from the secondfurnace into a press hardening tool; and g) forming and cooling thecomponent in the press hardening tool.
 7. The method according to claim4, wherein the component is heated in step a) to a temperature below theAc3 temperature.
 8. The method according to claim 4, wherein thecomponent is heated in step a) to a temperature above the Ac3temperature.
 9. The method according to claim 4, wherein the at leastone first sub-region is cooled in step c) by way of convection to atemperature below the Ac1 temperature.
 10. Use of at least one nozzleoperated at a positive pressure of at least 2 bar for convectivelycooling at least one first sub-region of a metal component so that atemperature difference of at least 100 K is set between the at least onefirst sub-region and at least one second sub-region of the component.